There is an important commercial need to obtain a color proof that will accurately represent at least the details and color tone scale of the image before a printing press run is made. In many cases, it is also desirable that the color proof accurately represents the image quality and halftone pattern of the prints obtained on the printing press. In the sequence of operations necessary to produce an ink-printed, full-color picture, a proof is also required to check the accuracy of the color separation data from which the final three or more printing plates or cylinders are made.
The generation of a proof involves imagewise transfer of material using infrared radiation from a donor to a receptor where the material can include, for example, colorants, pigments, dyes, and specialty pigments such as metallics. The transferred material can form an image, on the receptor, which can then be transferred to another surface. The color stability and transferability of the transferred material, or proof, has been limited, however, by the receptors currently available.
For example, known receptors contain a color bleaching agent for reduction of residual color from infrared dye (IR dye) used in the donor sheets. In one such receptor, the bleaching agent is combined with a binder material such as styrene butadiene in a single layer on a substrate material. While this receptor construction bleaches residual color from IR dye, the use of styrene butadiene for the single layer construction is problematic in at least two respects. First, the diphenyl guanidine bleaching agent has a tendency to crystallize in styrene butadiene. Second, styrene butadiene provides good bonding to the receptor support making it difficult to pull the styrene butadiene completely away from the support. This results in limited transferability following lamination, especially to thin paper stocks.
As an alternative to the styrene butadiene and diphenyl guanidine combination, a single layer of a binder such as polyvinyl butyral combined with a bleaching agent such as diphenyl guanidine has been used to provide a receptor having improved transferability. While polyvinyl butyral provides good release and transfer from the receptor support to a second support, however, complete bleaching of residual IR dye is not achieved until several days later. As a result, small color shifts are observed in a final proof. It is possible to condition the final proof such as by heating the final proof at 95° C. for 3 minutes, but this step increases both processing time and expense of the final proof.
A two-layer receptor construction has been proposed that includes a layer of styrene butadiene and a layer of polyvinyl butyral. This two-layer receptor construction has been problematic, however, because of insufficient bonding between the two layers.
Therefore, there exists a need for a thermal imaging receptor that provides both improved transferability and image color stability.